Chapter 5: Struts Work Flow
Struts principle and practice
上图是Struts的工作流程，前边我们提到，所有的请求都提交给ActionServlet来处理。
ActionServlet是一个FrontController，它是一个标准的Servlet，它将request转发给RequestProcessor来处理，
ActionMapping是ActionConfig的子类，实质上是对struts-config.xml的一个映射，从中可以取得所有的配置信息
RequestProcessor根据提交过来的url，如*.do，从ActionMapping 中得到相应的ActionForn和Action。然后将request的参数对应到ActionForm中，进行form验证。如果验证通过则调用Action的execute()方法来执行Action，最终返回ActionFoward。
ActionFoward是对mapping中一个foward的包装，对应于一个url
ActionForm使用了ViewHelper模式，是对HTML中form的一个封装。其中包含有validate方法，用于验证form数据的有效性。ActionForm是一个符合JavaBean规范的类，所有的属性都应满足get和set对应。对于一些复杂的系统，还可以采用DynaActionForm来构造动态的Form，即通过预制参数来生成Form。这样可以更灵活的扩展程序。
ActionErrors是对错误信息的包装，一旦在执行action或者form.validate中出现异常，即可产生一个ActionError并最终加入到ActionErrors。在Form验证的过程中，如果有Error发生，则会将页面重新导向至输入页，并提示错误。
Action是用于执行业务逻辑的RequsestHandler。每个Action都只建立一个instance。Action不是线程安全的，所以不应该在Action中访问特定资源。一般来说，应改使用 Business Delegate 模式来对Business tier进行访问以解除耦合。
Struts提供了多种Action供选择使用。普通的Action只能通过调用execute执行一项任务，而DispatchAction可以根据配置参数执行，而不是仅进入execute()函数，这样可以执行多种任务。如insert,update等。LookupDispatchAction可以根据提交表单按钮的名称来执行函数。
我们可以先回到刚才的例子，理解一下Struts的流程。
下面我们看Struts自带的example实例：
Chapter 6: Example 2: Login Application
Struts principle and practice
说明：实例二是Struts自带的example程序, 实现了登录，注册，修改功能
代码中大量应用了struts taglib，并且采用validator插件进行form的验证
但是代码树立了一个不好的榜样，即把大量的业务逻辑写在了action中。
部分代码如下：
登录：logon.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
// 声明Taglib
<%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>
<%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>
<html:html locale="true">
<head>
// bean是用来从ApplicationResource中读取i18n信息
<title><bean:message key="logon.title"/></title>
<html:base/>
</head>
<body bgcolor="white">
// 错误信息部分
<html:errors/>
// 登录form,action为logion.do
<html:form action="/logon" focus="username"
onsubmit="return validateLogonForm(this);">
<table border="0" width="100%">
<tr>
<th align="right">
<bean:message key="prompt.username"/>:
</th>
<td align="left">
<html:text property="username" size="16" maxlength="18"/>
</td>
</tr>
<tr>
<th align="right">
<bean:message key="prompt.password" bundle="alternate"/>:
</th>
<td align="left">
<html:password property="password" size="16" maxlength="18"
redisplay="false"/>
</td>
</tr>
<tr>
<td align="right">
<html:submit value="Submit"/>
</td>
<td align="left">
<html:reset/>
</td>
</tr>
</table>
</html:form>
// Validator插件,用于form验证
<html:javascript formName="logonForm"
dynamicJavascript="true"
staticJavascript="false"/>
<script language="Javascript1.1" src="staticJavascript.jsp"></script>
</body>
</html:html>
struts-config.xml配置
<form-beans>
<!-- Logon form bean -->
<form-bean name="logonForm"
type="org.apache.struts.validator.DynaValidatorForm">
<form-property name="username" type="java.lang.String"/>
<form-property name="password" type="java.lang.String"/>
</form-bean>
<!-- Subscription form bean -->
<form-bean name="subscriptionForm"
type="org.apache.struts.webapp.example.SubscriptionForm"/>
</form-beans>
<action-mappings>
<!-- Edit mail subscription -->
<action path="/editSubscription"
type="org.apache.struts.webapp.example.EditSubscriptionAction"
attribute="subscriptionForm"
scope="request"
validate="false">
<forward name="failure" path="/mainMenu.jsp"/>
<forward name="success" path="/subscription.jsp"/>
</action>
...
subscriptionForm 是一个标准的ActionForm,其中reset方法用于清除form的值,validate方法用于验证
public final class SubscriptionForm extends ActionForm {
// The maintenance action we are performing (Create or Edit).
private String action = "Create";
// Should we auto-connect at startup time?
private boolean autoConnect = false;
// The host name.
private String host = null;
private String password = null;
private String type = null;
private String username = null;
public String getAction() {return (this.action); }
public void setAction(String action) { this.action = action; }
public boolean getAutoConnect() { return (this.autoConnect); }
public void setAutoConnect(boolean autoConnect) { this.autoConnect = autoConnect; }
public String getHost() {return (this.host); }
public void setHost(String host) { this.host = host; }
public String getPassword() {return (this.password); }
public void setPassword(String password) { this.password = password; }
public String getType() {return (this.type); }
public void setType(String type) { this.type = type; }
public String getUsername() {return (this.username); }
public void setUsername(String username) { this.username = username; }
/**
* Reset all properties to their default values.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
*/
public void reset(ActionMapping mapping, HttpServletRequest request) {
this.action = "Create";
this.autoConnect = false;
this.host = null;
this.password = null;
this.type = null;
this.username = null;
}
/**
* Validate the properties that have been set from this HTTP request,
* and return an <code>ActionErrors</code> object that encapsulates any
* validation errors that have been found. If no errors are found, return
* <code>null</code> or an <code>ActionErrors</code> object with no
* recorded error messages.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
*/
public ActionErrors validate(ActionMapping mapping,
HttpServletRequest request) {
ActionErrors errors = new ActionErrors();
if ((host == null) || (host.length() < 1))
errors.add("host",
new ActionError("error.host.required"));
if ((username == null) || (username.length() < 1))
errors.add("username",
new ActionError("error.username.required"));
if ((password == null) || (password.length() < 1))
errors.add("password",
new ActionError("error.password.required"));
if ((type == null) || (type.length() < 1))
errors.add("type",
new ActionError("error.type.required"));
else if (!"imap".equals(type) && !"pop3".equals(type))
errors.add("type",
new ActionError("error.type.invalid", type));
return (errors);
}
}
logonAction
public final class LogonAction extends Action {
/**
* Process the specified HTTP request, and create the corresponding HTTP
* response (or forward to another web component that will create it).
* Return an <code>ActionForward</code> instance describing where and how
* control should be forwarded, or <code>null</code> if the response has
* already been completed.
*
* @param mapping The ActionMapping used to select this instance
* @param form The optional ActionForm bean for this request (if any)
* @param request The HTTP request we are processing
* @param response The HTTP response we are creating
*
* @exception Exception if business logic throws an exception
*/
public ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
// Extract attributes we will need
Locale locale = getLocale(request);
MessageResources messages = getResources(request);
User user = null;
// Validate the request parameters specified by the user
ActionErrors errors = new ActionErrors();
String username = (String)
PropertyUtils.getSimpleProperty(form, "username");
String password = (String)
PropertyUtils.getSimpleProperty(form, "password");
UserDatabase database = (UserDatabase)
servlet.getServletContext().getAttribute(Constants.DATABASE_KEY);
if (database == null)
errors.add(ActionErrors.GLOBAL_ERROR,
new ActionError("error.database.missing"));
else {
user = getUser(database, username);
if ((user != null) && !user.getPassword().equals(password))
user = null;
if (user == null)
errors.add(ActionErrors.GLOBAL_ERROR,
new ActionError("error.password.mismatch"));
}
// Report any errors we have discovered back to the original form
if (!errors.isEmpty()) {
saveErrors(request, errors);
return (mapping.getInputForward());
}
// Save our logged-in user in the session
HttpSession session = request.getSession();
session.setAttribute(Constants.USER_KEY, user);
if (log.isDebugEnabled()) {
log.debug("LogonAction: User '" + user.getUsername() +
"' logged on in session " + session.getId());
}
// Remove the obsolete form bean
if (mapping.getAttribute() != null) {
if ("request".equals(mapping.getScope()))
request.removeAttribute(mapping.getAttribute());
else
session.removeAttribute(mapping.getAttribute());
}
// Forward control to the specified success URI
return (mapping.findForward("success"));
}
/**
* Look up the user, throwing an exception to simulate business logic
* rule exceptions.
*
* @param database Database in which to look up the user
* @param username Username specified on the logon form
*
* @exception ModuleException if a business logic rule is violated
*/
public User getUser(UserDatabase database, String username)
throws ModuleException {
// Force an ArithmeticException which can be handled explicitly
if ("arithmetic".equals(username)) {
throw new ArithmeticException();
}
// Force an application-specific exception which can be handled
if ("expired".equals(username)) {
throw new ExpiredPasswordException(username);
}
// Look up and return the specified user
return ((User) database.findUser(username));
}
}
[url=http://localhost:83/index.jsp][/url]
